The present invention relates to a golf club head and a method for producing the same, and more particularly relates to improvements in mechanical and dimensional characteristics of a golf club head made of a metallic material such as high-tensile steel.
A metallic golf club head is in general produced conventionally from a metallic material such as stainless steel alloys, aluminum alloys, titanium alloys and beryllium alloys by means of precision casting. Due to employment of a casting process in production, casting defects and local concentration of components are unavoidably present in the product. They concur to degrade the mechanical characteristics of the product such as proof stress and tensile strength of the product. Such disadvantages are further amplified by relatively coarse nature of crystal gains special to the precision casting.
Because of the low level of the mechanical characteristics, it is difficult to form a thin shell construction and, as a consequence, it is difficult to enlarge the entire size of the product without increase in weight. As well known in the art, a small golf club head is very poor in its sweet spot, which results in unstable flight of balls strikes by the golf club head.
In an attempt to avoid such disadvantages derived from the casting process, it is proposed as an alternative to unit together by welding a number of sectional, pieces which are produced by processes other than precision casting. In this case, the sectional pieces are produced, for example, by forging or pressing.
One example of such an assembly type golf club head is disclosed in Japanese Utility Model Publication (JUMP) Sho. 61-33971, A golf club head of this earlier proposal is made up of two sectional pieces, i.e. a face section provided with a front hosel half and a rear section provided with a rear hosel half. When the face and the rear sections are united together, the hosel halves form a hosel to hold a shaft. In the case of this example, the hosel halves are united together by welding which tends to generate strain in the body of the golf club head. Generation of such strain during production may disorder the originally designed lie and loft angles of the golf club head.
Another example of the assembly type golf club head is disclosed in Japanese Patent Laid-open (JPLO) Sho. 59-20182. A golf club head of this earlier proposal is made up of four sectional pieces, i.e. a face section, a sole section, a crown section and a hosel section. Since the hosel section is separate from other sections, welding has to be applied all around the hosel section during assembly. Such overall welding on the hosel section inevitably generates great strain in the body of the golf club head which seriously degrades accuracies of the lie and loft angles, Presence of a welded joint between the hosel and face sections lowers mechanical strength of the entire construction. Stress concentration on many weld lines during use may incur accidental breakage of the golf club head,
The other example of the assembly type golf club head is disclosed in JUMP Sho. 61-33970. A golf club head of this earlier proposal is made up off four sectional pieces, i.e. a face section, a sole section provided with a rear hosel half, a crown section provided with a front hosel half and a shaft insert section. An inner reinforcement is attached to the sole section. Presence of many weld lines develops high degree of strain in production and lowers resistance against mechanical shocks during use of the product. Intricate operations are needed for uniting the sectional pieces together in production. A like prior art example is found in JUMP Sho. 61-33972 too.